Switching mechanisms



Dec. 30, 1958 G. J.- LYNCH 2,866,861

SWITCHING MECHANISMS Filed April 25, 1956 INVENTOR. GEORGE J. LYNCH BY4A A rroR/vys United States Patent SWITCHING MECHANISMS George J. Lynch,Bloomfield, N. 1., assignor to Mycalex Electronics Corporation, Clifton,N. 3., a corporation of New York Application April 25, 1956, Serial No.580,524

7 Claims. (01. 200-41) This invention relates to switching mechanismsand particularly to high speed mechanisms for use in telemeteringsystems in which a large number of continuous switching operations mustbe carried out. More particularly, this invention relates to an improvedbrush assembly for operation in a switching mechanism of the typedescribed.

Switching mechanisms of the type mentioned above are known in the art.The conventional types heretofore known have been unable to perform alarge number of continuous simultaneous switching operations withoutoccupying relatively large spaces and without being relativelycomplicated, thereby limiting their use to relatively large mechanisms.Switching mechanisms of the type described herein normally employ acommutator in association with brushes which move relative to thecommutator to collectively and successively close and open a pluralityof circuits. Such mechanism must be arranged to be relatively free frombrush bounce during the switching operations and must have relativelyuniform electrical properties in order to maintain the noise levelproduced by brush bounce and non-uniform electrical properties at aminimum. When the noise level exceeds a certain percentage of the signallevel, the signal becomes unintelligible and thereby eliminates thepossibility of supplying information to other portions of thetelemetering apparatus.

As stated above, the major sources of noise in switching devices of thetype described are brush or contact bounce and non-uniform electricalproperties. The latter circumstance commonly arises due to the depositof brush material on the contact material of the commutator or due to awearing or abrading of the contact material.

One object of the present invention is the provision of a switchingdevice of the type described which has substantially noise-freeoperation during a large number of sWitching operations.

Another object of the present invention is the provision of a new andimproved brush assembly for a switching mechanism of the type describedwhich is adapted to maintain electrically uniform properties for theswitching mechanism throughout a large number of switching operations.

Another object of the present invention is the provision tures of thepresent invention will be more fully understood from the followingdescription taken in connection with the accompanying illustrativedrawings.

In the drawings:

Fig. 1 is a side elevational view of a switching mechanism embodying thepresent invention with some parts Zfihhfifii Patented Dec. 30,

designated by the reference numeral 10. Such a switching mechanismcomprises a housing 12 including a base 14- and a U-shapedlongitudinally extending member 16 which are held together in anysuitable manner such as by screws 18. Disposed within the housing are amotor (not shown), a gear train 20 connected to the output shaft 22 ofsaid motor, a shaft 24 which is the output shaft of the gear train, abrush assembly 26 mounted on said shaft 24 for rotation therewith and acommutator plate 28 which is in operative relationship with the brushassembly 26.

Particularly, the gear train output shaft 24 is journaled in two bearingplates 30 which are fixed to the base 14 as by screws 32 which extendthrough reflex portions 34 on the bearing plates 30. The commutatorplate 28 comprises a modified triangular plate 36 of insulating material into which is molded a slip ring 38 and a plurality of spacedcontacts 40 which are arranged in a circle concentric with said slipring. Contacts 40 are preferably spaced from each other a distance whichis much less than the width of the brushes forming part of the brushassembly 26 which will be described hereinafter. Preferably, eachcontact 40 is disposed as close to its adjacent contacts as is permittedby consideration of good insulation therebetween, it is believed clearthat the closer the contacts are to each other, the less brush bouncethere will be as the brush moves from one contact to another. Thecommutator plate 36 is provided adjacent its apexes with apertures 42through which support rods 44 extend for supporting the commutatorplate. The support rods 44 are fixed at each end to the bearing plates30 whereby to hold the commutator plate in fixed relation relative tosaid bearing plate. For proper securement of the com mutator plate tothe supporting rods 44 collars 46 are mounted on the support rods andabut against adjacent surfaces of the commutator plate whereby toprevent movement of said plate longitudinally of said support rods.

Commutator plate 36 is preferably made of a vitreomicaceous materialsuch as ceramoplastic or glass-bonded mica. This class of materials ispreferred since it is the only known class of insulating material whichhas sufficient dimensional stability to maintain the slip ring 38 andthe contacts 46 in proper spaced relationship under the range ofoperating conditions to which the switching mechanism is subjected.Preferably, the slip ring and the contacts are fixed to the commutatorplate 36 as by molding and the commutator plate 36 has a coefiicient' ofthermal expansion which is substantially equal to that of the slip ringand the contacts whereby to maintain the slip ring and contacts in fixedrelationship throughout wide range of temperatures. The slip rings andcontacts are preferably made of rhodium plated coin silver and areprovided with extremely smooth pitfree surfaces.-

in the art that the surfaces of all the contacts 40 are coplanar and theplane defined by the surface of the contacts 48 is preferably coplanarwith the surface of the slip ring 38,:although' this isn'ot'necessary.

As stated hereinbefore, the output shaft- 24'of the gear train 28 isjournaled in the bearing plates 30. Shaft 24 extends through a centralaperture 51 in commutator plate 36, the central aperture beingconcentric with the slip ring 38 and the circle defined by the contacts40.

According to the present invention the brush assembly 26 comprises asupport member 54 having a central aperture 56 which is adapted toreceive shaft 24. Adjacent the central aperture 56, support member 54 isprovided with a pair of longitudinally extending slots 58 and a pair ofclamping screws 60 are threadedly engaged with the member 54 and extendtransversely of said member and through slots 58. It will b'e obvious tothose skilled in the art that the'support member 54'n1 ay be fixed-toshaft 24 by tightening the clampin'gscrews 66 whereby to take advantageof the resiliency of the member54- which is preferably made ofa'metallic material. Fixed adjacent one end of support member 54 as by ascrew 64 is a brush arm 62. Preferably, brush arm 62 is insulated fromsupport member 54 as by an insulating washer 66 interposed between thebrush arm and the support member. Brush arm 62 preferably has twoangularly related portions 68 and 70, the portion 68 being adapted tocarry a brush 72 and the portion 74) being provided with a terminal orbinding post 74. The brush arm 62 may be made of any good conductionmaterial such as beryllium copper, Phosphor bronze, and so forth.However, in accordance with one of the objects of the present invention,the brush arm 62 is made of two substantially coextensive portions 76and 78, the portion 76 being made of a relatively resilient materialsuch as spring steel and the portion 78 being made of a good conductingmaterial such as beryllium copper. The portions 76 and 78 of the brusharm 62 are preferably joined together so as to be substantiallyintegralas by soldering or the like throughout most of the brush arm.However, adjacent the end 80 of the brush arm 62' which end is adaptedto carry the brush 72, the portions 76' and 78 are spaced from oneanother and a piece of resilient material such as silicone rubber orrubber is interposed between said portions 76 and'78 whereby to absorbmost of the bounce caused by brush'72 moving from contact 40 to contact40. For reasons which will become clear hereinafter, brush 72 ispreferably made of a relatively soft conducting material such as silvergraphite and preferably silver graphite in a range of 60% to 40% silverand 40% to 60% graphite, respectively. Most preferably, bru'sh "72 ismade of a silver graphite composition including 44% silver and 56%graphite.

Secured adjacent the opposite end of support member 54 as by a screw 84is brush member 85 comprising a pair of angularly related brush arms 86and 88 which carry brushes 9t) and 92, respectively, both of saidbrushes being in sliding relationship With the slip ring 38. Brush arms86 and 88 are preferably insulated from the member 54 as by aninsulating washer 94. The brush arms 86' and 88 are preferably integraland made of any suitable conducting material such as beryllium copperalthough Phosphor bronze or other suitable conducting material may beemployed. Of course, the arms 86 and 88 may be formed of separate piecesand joined together after manufacture thereof. Preferably, theconnection between the two arms is electrically conducting whereby tomaintain said arms at the same electrical potential, although one ofsaid arms may be insulated from the other.

In accordance with the present invention, one of the brushes, preferablybrush 90, is made of a relatively soft brush material, such as silvergraphite. In order to obtain best results, the silver graphite should becomposed of between 40% to 60% silver and 60% to 40% graphite andpreferably a silver graphite composition including approximately 44%silver and 56% graphite. The brush 92 is preferably made of a relativelyhard brush material such as white gold although other metallic brushmaterials may be used. One example of a white gold composition suitablefor the present application is as follows:

Percent Gold 56.2 Copper 22.8 Zinc 7.4 Nickel 13.6

Since, as will become more clear hereinafter when the operation of thepresent invention is described, the brush assembly is employed tosuccessively close circuits between each of the contacts 40 and the slipring38, means must be provided to conduct electrical current from thebrush arm 62 to the brush member 85. As shownherein, a wire conductor 96is employed to perform this func' tion. Specifically, wire 96 isconnected to portion 70 of brush arm 62 as by terminal 74 and is securedin electrical conducting relationship with brush member as by a terminal98 secured to said brush member.

In operation, electrical impulses are supplied to con tacts 40 and toslip ring 38. Preferably, brush 72 is proportioned to be larger than thespacing between the contacts 40 whereby'it will bridge each adjacentpair of contacts as it moves from one to the other. Accordingly, ifelectrical impulses were supplied to adjacent contacts cross talk wouldresult which, unless a gating circuit were employed, would beundesirable. In order to obviate the possibility of crosstalk it isdesirable that electrical impulses be supplied only to every othercontact 40 whereby the intermediate unenergized contacts are employedmerely as a bridge for the brush 72 to move from one energized contactto another. In this manner there will be no cross talk. Accordingly,when the motor is energized to rotate shaft 24 and thereby rotate thebrush assembly, brush 72 will move successively fromone contact toanother and brushes 9t) and 92 will move relative to slip ring 38 inelectrical conducting sliding relationship therewith. Each time brush 72engages anenergized contact 40, a circuit will be closed throughconductor 96'whereby to supply certain information to electro responsiveapparatus not forming'part'of the inven tion. The novel brush assemblyhas been found to operate in such a manner as to prevent non-uniformconduction'to' arise between different portions of the slip ring 38 andthe brushes and 92. By eliminating the possibility of non-uniformconductive properties, one of the major sources of signal noise iseliminated. Applicant is of the belief that this highly desirable resultemanates from the depositing of silver graphite on the rhodium platedcoin silver graphite deposited from the brush 90 by the white goldbrush92. The depositing of the silver graphite on the surface of the slipring appears to fill up pits or other surface irregularities on saidslip ring whereby to render the entire slip ring uniform bothmechanically and electrically. The white gold brush which follows thesilver graphite brush, appears to sweep away any excessive amount ofsilver graphite deposited on the slip ring 38. Any excess of silvergraphite would naturally result in irregular electrical properties and,due to subsequent contamination with foreign matter, a general increasein the resistance be tween the brushes and the slip ring. Brush 92eliminates this possibility. Furthermore, the silver graphite tends tolubricate the slip ring and thereby reduce abrasion thereof. Moreover,by employing two brushes 90 and 92 in engagement with the slip ring 38,if one of said brushes for any reason were to bounce so as to increasethe resistance between said brush and the slip ring 38,

the probability is that the other of said brushes would aseasei remainin electrical conducting relationship with the slip ring. Accordingly,by employing two space brushes, the variation in resistance between thebrush arm 85 and the slip ring 38'resulting from brush bounce issubstantially reduced from that which would normally be expected if asingle brush were employed;

Another highly desirable feature of the present invention is thepressure with which the brushes engage the slip ring and contacts.Heretofore, in order to achieve long life for switches of this type, thebrush pressures were maintained at an extremely low level in order toreduce possible abrading or wear on the brushes and contacts. This lowcontact pressure resulted in a tendency toward excessive brush bouncegiving rise to extremely high noise levels. Due to the improvement inthe commutating characteristics of the present telemetering switch, ithas been found that the brush pressures may be greatly increased overthat heretofore employed, which increase results in a substantialreduction in brush bounce and, accordingly, a reduction in noise.Specifically, it has been found that upon original fabrication of thecommutating switch disclosed herein, the brush arms 68, 86 and 88 may beadjusted so that the brushes 72, 90 and 92, respectively, evert 120pounds per square inch, 74 pounds per square inch and 68 pounds persquare inch, respectively, on the contacts and slip ring. Of source,these pressures may be varied somewhat without departing from thishighly desirable feature of the present invention. Thereafter, theswitch may be operated for a break-in period of from one to seven days.Upon the completion of the break-in period, the brushes, contacts andslip rings are cleaned. The cleaning may be effected by manuallyrotating the brush assembly in a direction opposite to its normaldirection of rotation (that is, manually rotating the brush assembly ina clockwise direction as viewed in Fig. 2) or by subjecting thecommutating disc and brushes to a jet of compressed air or by. polishingthe contacting surfaces with crocus cloth or by lubricating thecontacting surfaces with petroleum jelly containing finely powderedgraphite, or any combination of these methods. After the contactingsurfaces have been cleaned as indicated above, the switch is reassembledwithout any adjustment of the brush pressures and the commutator may beoperated for at least one thousand hours with a substantially noise-freesignal and with no further attention. At the end of this operationalperiod, if excessive noise appears, the contacting surfaces may berecleaned and the successive periods of operation and cleaning may beobserved until the brushes are no longer fit for use. Moreover, when thebrushes have deteriorated to the point where they are no longer useful,it will be found that the commutator disc and particularly thecontacting surfaces of the contacts 40 :and slip ring 38 are still inuseful condition.

Accordingly, all that need be done to continue using the switch is toreplace the old brush assembly with a new brush assembly.

It will be understood that the novel brush assembly disclosed herein maybe used with telemetering switches now in use, replacing older and lesssatisfactory brush assemblies.

Although I have herein shown and described only one form of the presentinvention and have suggested various changes and modifications therein,it will be understood that various other changes and modifications maybe made therein within the scope of the appended claims withoutdeparting from the spirit and scope of this invention.

Having now described my invention, what I claim as new and desire tosecure by Letters Patent is:

1. In an electric device, a first conducting means, a second conductingmeans movable relative to said first conducting means, said secondconducting means comprising spaced brushes in sliding moving engagementwith said first conducting means along the same path thereon,

one of said spaced brushes being relatively hard and another of saidspaced brushes being relatively soft.

2. In an electric device, first and second conducting means, and brushmeans movable relative to said first and second conductingmeans, saidbrush means including a first brush in sliding moving engagement withsaid first conducting means and second and third spaced brushes inmovable engagement with said second conducting means along the same paththereon, said second brush being relatively hard and said third brushbeing relatively soft.

3. In an electric device, first and second conducting means, and brushmeans movable relative to said first and second conducting means, saidbrush means including a first brush in movable engagement with saidfirst conducting means and second and third spaced brushes in movableengagement with said second conducting means, said second brush beingrelatively hard and said third brush being relatively soft, said secondconducting means being harder than said second brush.

4. In an electric device, a first conducting means comprising aplurality of circularly arranged spaced contacts, a second conductingmeans comprising a ring of conducting material arranged concentricallywith said first conducting means, means for insulating said firstconducting means from said second conducting means, and brush meansrotatably movable relative to said first and second conducting means,said brush means including a first brush in sliding engagement with saidfirst conducting means and second and third spaced brushes in slidingrelation with said second conducting means, and said second brush beingmade of relatively soft conducting material and said third brush beingmade of relatively hard conducting material.

5. In an electric device, a first conducting means comprising aplurality of circularly arranged spaced contacts, a second conductingmeans comprising a ring of conducting material arranged concentricallywith said first conducting means, means for insulating said firstconducting means from said second conducting means, and brush meansrotatably movable relative to said first and second conducting means,said brush means including a first brush in sliding engagement with saidfirst conducting means and second and third spaced brushes in slidingrelation with said second conducting means, said second and thirdbrushes being electrically connected to each other.

6. In an electric device, a first conducting means comprising aplurality of circularly arranged spaced contacts, a second conductingmeans comprising a ring of conducting material arranged concentricallywith said first conducting means, means for insulating said firstconducting means from said second conducting means, and brush meansrotatably movable relative to said first and second conducting means,said brush means including a first brush in sliding engagement with saidfirst conducting means and second and third spaced brushes in slidingrelation with said second conducting means, said second brush being madeof relatively soft conducting material and said third brush being madeof relatively hard conducting material, said second and third brushesbeing electrically connected to each other.

7. In a commutating device having a commutator disc including a contactring provided with terminal means, a plurality of spaced contactsarranged in a circle spaced from and concentric with said contact ring,one of said contacts having another terminal means associated therewith,said contact ring and said spaced contacts being molded in a plateformed of vitreo-micaceous material whereby to insulate said spacedcontacts from each other and from said contact ring, and a rotatableshaft concentric with said contact ring; brush means for successivelyconnecting said spaced contacts to said contact ring, comprising amember fixed to said shaft for rotation therewith, a first brush armcarried by said member for rotation therewith, a first brush carried bysaid first brush arm and being successively slidably electricallyengageing a brush thereon, said SQCOlldsbI'llSh armxbeingzcarrieid bysaid member for rotationstherewith; tsaid brushes being carried by saidsecond brush arm being spaced frornsone another and being in slidingengagement with said contact ring, one of said brushes on saidrsecondbrush:armv.being relatively soft andtheother of said brush :arms on.said second brush being relatively hard;

Referenceszfiited in. the'file :of .ihispatent;

' UNIT EDSTATESiPAT-ENTS? Sehi'fie'rt Ai1g.;,5 1919. Wootton Dec. 1 3,19211 Clurman 'Mar. 25; 193.0

